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Using a series of cosmological simulations that includes one dark-matter-only (DM-only) run, one gas cooling-star formation-supernova feedback (CSF) run and one that additionally includes feedback from active galactic nuclei (AGNs), we classify the large-scale structures with both a velocity-shear-tensor code (Vweb) and a tidal-tensor code (Pweb). We find that the baryonic processes have almost no impact on large-scale structures - at least not when classified using aforementioned techniques. More importantly, our results confirm that the gas component alone can be used to infer the filamentary structure of the universe practically un-biased, which could be applied to cosmology constraints. In addition, the gas filaments are classified with its velocity (Vweb) and density (Pweb) fields, which can theoretically connect to the radio observations, such as H I surveys. This will help us to bias-freely link the radio observations with dark matter distributions at large scale.
Left-hand panel: The relative volume (_V), mass (_M) and consistency (_F) fraction difference between the DM component and all matter; Right-hand panel: The relative fraction difference between the gas component and all matter. Upper row shows the Vweb results, while bottom row is from the Pweb code.
Left figure shows the projected cosmology structures for a slice of the simulations from the Vweb method: knots, filaments, sheets and void regions, which are shown as red, green, blue and black colours, respectively. The three columns from left- to right-hand side show the results from the DM-only, CSF and AGN runs. The classification results with all matter, DM, gas and stellar components are shown from the top to bottom rows, respectively. The left-hand lower three panels show the projected all matter, gas and stars densities from the CSF run, respectively.
Cui, Weiguang; Borgani, Stefano; Murante, Giuseppe, 2014, MNRAS, 441, 1769C
Following the work of Cui et al, 2012, we further included AGN feedback model in the cosmology simulation and investigate its effects on the halo mass function. In addition to that, we also published a Python spherIcAl Overdensity halo identification code - PIAO (https://github.com/ilaudy/PIAO). For both FoF and SO haloes, the effect of AGN feedback is that of suppressing the HMFs to a level even below that of dark matter (DM) simulations. The ratio between the HMFs in the AGN and in the DM simulations is ~0.8 at overdensity Δc = 500, a difference that increases at higher overdensity Δc = 2500, with no significant redshift and mass dependence. A decrease of the halo masses ratio with respect to the DM case induces the decrease of the HMF in the AGN simulation. The shallower inner density profiles of haloes in the AGN simulation witnesses that mass reduction is induced by the sudden displacement of gas induced by thermal AGN feedback. We provide fitting functions to describe halo mass variations at different overdensities, which can recover the HMFs with a residual random scatter ≲5 per cent for halo masses larger than 1013 h-1 M⊙.
Left figure: SO halo Mass difference. It is clear that AGN feedback decreases halo mass from ~20% to a few percent with almost no redshift dependence.
Right figure: SO halo mass function difference, which agrees with the halo mass difference.
Cui, Weiguang; Borgani, Stefano; Dolag, Klaus; Murante, Giuseppe; Tornatore, Luca, 2012, MNRAS, 423, 2279C
Using a series of three cosmology simulations with 10243 particles each within a simulation boxsize of 410 h-1 Mpc, which share the same initial conditions, we investigate the baryon effects on the spherical overdensity halo mass functions with Δc= 200, 500 and 1500. These three simulations include a dark-matter-only simulation; one with non-radiative physics, which gas is only heated by gravitational processes; one has radiative cooling, star formation and kinetic feedback in the form of galactic ejecta triggered by supernova explosions.
We investigate the baryon effects on the halo mass and halo mass function. We found that assuming a constant mass shift to rescale the HMF from the hydrodynamic to the DM simulations, brings the HMF difference with respect to the DM case to be consistent with zero. Our results have interesting implications for cosmological applications of future large surveys of galaxy clusters.
As shown in the right figures, the fractional difference between halo masses in the hydrodynamical and in the DM simulations is almost constant with little redshift dependence, at least for more massive haloes. In that range, mass increase in the hydrodynamical simulations is of about 4-5 per cent at Δc= 500 and ˜1-2 per cent at Δc= 200. Quite interestingly, these differences are near for both radiative and non-radiative simulations at Δc= 500 and 200.
Right figures show the halo mass function changes between the hydro-simulations and the DM runs for different overdensities (left panel) and different redshifts (right panel). In agreement with the halo mass changes, the halo mass function show similar changes for Δc= 500 and 200 with weak redshift dependence.
Cui, Weiguang; Liu, Lei; Yang, Xiaohu; Wang, Yu; Feng, Longlong; Springel, Volker, 2008, ApJ, 687, 738C
We proposed a particular function --- the scale functions of Daubechies wavelet transformations in performing the mass assignment that can minimize the sampling effects of the window function, which normally use the nearest grid point (NGP), cloud-in-cell (CIC) or triangular-shaped cloud (TSC) assignments. Using our new assignment method, we test the data from the Millennium Simulation and show that the true power spectrum of dark matter can be accurately measured at a level better than 2% up to k = 0.7kN, without applying any deconvolution processes. The new scheme is especially valuable for measurements of higher order statistics, e.g., the bispectrum, where it can render the mass assignment effects negligible up to comparatively high k.
Right figure shows the power spectrum from window functions of NGP, CIC and TSC, as well as the new Daubechies wavelets. Lower right panel proves that our method works perfectly as expected.
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